STD Awareness: June Is National Congenital Cytomegalovirus Awareness Month

Pop quiz: Can you name the virus that most commonly infects developing fetuses when they are still in the womb?

Here’s a hint: June is National Congenital Cytomegalovirus Awareness Month.

In case that clue didn’t make it obvious enough, I’ll tell you the answer. The most common infection among developing fetuses is caused by a virus you might not have heard of: cytomegalovirus, or CMV. Around 30,000 children are born with this infection every year, and some of these babies will go on to develop serious problems because of it. National Congenital Cytomegalovirus Awareness Month is a time to learn about how CMV can affect pregnancy.

Cytomegalovirus can damage developing brain cells early in an embryo’s gestation.

This year, it might be of even greater interest, given the parallels that can be drawn between CMV and Zika virus, the emerging pathogen that has been dominating headlines lately. First of all, both CMV and Zika virus can be transmitted sexually, though they are not the first things you think of when the topic of STDs comes up, as they are overshadowed by more famous sexually transmitted viruses like herpes and human papillomavirus. While many of us are infected with CMV as children, we can also be infected as adults, often through sexual transmission — the virus can be found in cervical and vaginal secretions, saliva, and semen. The sexual transmission of Zika virus is not as well understood, but we know it can be found in semen, and there are documented cases of men passing the virus to sex partners through vaginal and anal intercourse. It might even be transmitted from a male to a partner by oral sex.

Second of all, both CMV and Zika virus are associated with birth defects. However, while the connection between CMV and birth defects has been known to us for decades, it was only in April that the Centers for Disease Control and Prevention concluded that Zika virus can cause fetal brain defects (though we’re still waiting for conclusive proof). Microcephaly is probably the most infamous of the birth defects associated with Zika virus, as well as CMV, but it’s not well defined. When you get down to it, though, microcephaly just refers to an abnormally small head, which itself might be indicative of a brain that has failed to develop fully.

While a CMV infection usually doesn’t have symptoms, 33 percent of people infected for the first time during pregnancy will pass the virus to the fetus. The virus can infect a fetus via two main routes of transmission: (1) direct transmission, in which CMV is attached to semen and infects the embryo directly, and (2) transplacentally, in which the virus crosses the placenta to infect the fetus in the uterus.

About 1 in 150 U.S. babies is congenitally infected with CMV, which simply means that the infection happened during pregnancy. Luckily, most babies infected with CMV will be fine, but around 20 percent of them will have symptoms, such as jaundice; rash; problems with their liver, lung, or spleen; microcephaly or low birth weight, and seizures. Permanent disabilities are also possible, and these include blindness, deafness, and developmental disabilities. In very rare cases, congenital CMV can be fatal.

While we still don’t know how Zika virus can cause brain damage in a developing fetus, we’ve known since at least the 1960s that CMV during pregnancy can result in microcephaly. It is thought that CMV can infect brain cells very early in a pregnancy, interfering with subsequent development and resulting in serious abnormalities. The earlier in pregnancy a CMV infection occurs, the higher the risk is to the developing fetus, as damaged cells can pass on errors as they divide. Perhaps we’ll soon discover that Zika virus operates similarly. The risk to babies is lower when they catch CMV during birth or through breastfeeding, at which time their brains are more fully formed than they are during the early stages of gestation.

Bringing your infant to doctor’s appointments is important. When a baby is 2 or 3 weeks old, he or she can be tested for congenital CMV — but the test results won’t be as reliable if you wait until the child is older. While only 0.1 percent of U.S. babies will have permanent problems caused by CMV, knowing that your baby has been infected allows you to discuss antiviral treatments with a doctor, and to monitor your child’s health closely so he or she can receive early treatment if necessary.

About Anna C.

Anna first volunteered for Planned Parenthood as a high school student in the 1990s. Since then, she has received a bachelor’s degree from UC Berkeley and a master's degree in epidemiology from the University of Arizona. As an ode to her fascination with microbes, she writes the monthly STD Awareness series, as well as other pieces focusing on health and medicine.